This invention relates to pressure and differential pressure detectors and transmitters, and is particularly directed to pressure and differential pressure detectors suitable for use within the containment vessel of a nuclear power plant, in which, under catastrophic plant conditions, the detector could be exposed to temperatures up to 500.degree. F. and external pressures of up to 500 psig.
Pressure and differential pressure transmitters are currently employed in nuclear power plants to provide a remote indication of critical pressure or pressure differentials, for example, pressure differences in the primary fluid within the nuclear reactor loops or between the inlet and outlet headers of a nuclear steam generator. These measurements are used to monitor the performance of the nuclear power plant, and the reliable and accurate operation of such detector is necessary to ensure safe operations management of the nuclear power plant.
These pressure detectors normally employ a housing in which a pressure bellows is disposed, with pressure ports provided to permit fluid communication between the inside and outside of the pressure bellows. A shaft connected to the pressure bellows then displaces the movable core of a linear variable differential transformer (LVDT) which is also disposed within the detector housing. An AC signal is provided to the primary winding of this differential transformer, and the displacement of the core affects the relative strength of signals derived from A and B secondary windings of this differential transformer. The relative strengths of these signals indicate the differential pressure measured by the pressure detector.
However, such previous pressure and differential pressure detectors and transmitters have not been suitably hardened to withstand external pressures far in excess of normal ambient pressures, nor have these detectors been designed to withstand the temperature of impinging live steam. In addition, such previous pressure detectors have not been provided with any means to compensate for signal drift caused by changes in temperature of the LVDT, and, consequently, such detectors and transmitters have not been able to provide accurate measurements of pressure over wide ranges of environmental temperatures.